The present invention relates to an alternating-current motor intended to drive a pump or a compressor.
It is particularly suitable for the production of pumping units which are immersed in a liquid.
It finds its application especially in the oil industry for pumping fluids at the bottom of production wells for hydrocarbons in liquid, gaseous or multi-phase form.
The electric motors which are most widely used are single-phase or multi-phase asynchronous alternating-current motors. Their structure is described in TECHNIQUES DE L""INGENIEUR (ENGINEERING TECHNOLOGY), a treatise on electrical engineering, Volume D 3 II Chapter D 3 490 Asynchronous motorsxe2x80x94choice and related problems.
According to this document, asynchronous alternating-current motors essentially include a stator and a rotor.
The stator consists of coiled windings of conducting wires distributed within a yoke ring forming a framework and housed within a magnetic circuit supported by this yoke ring. This magnetic circuit is formed by stacks of laminations in the form of circular crowns into which slots are cut parallel to the axis of the yoke ring and in which the conducting wires of the coiled windings are housed.
Within the crown-shaped magnetic circuit formed by the stack of laminations is placed the cylindrical-shaped rotor which includes a rotational shaft supported by a support bearing which is integral with the yoke ring of the stator.
The most widespread type of rotor is the squirrel cage rotor, the circuit of which consists of conducting bars regularly spaced between two metal crown rings forming the extremities.
This squirrel cage is inserted within a magnetic circuit consisting of disks stacked on the rotational shaft.
With this type of motor, since the distances between the windings of the stator are very short, they cannot be supplied with very high voltages and the installation of insulators is an intricate matter.
The same problem is posed for the insulation of the windings with respect to the laminations of the stator circuit.
For certain applications, for example for raising water from a water table or hydrocarbons laid down at the bottom of a well, the shaft of the motor is coupled to a pump and the motor-plus-pump assembly is immersed in the fluid to be pumped.
In this case, the space between the rotor and the stator is filled with liquid, which further accentuates the problems of electrical insulation set out above.
One known solution consists in separating the motor from the pump, but requires the use of a dynamic sealing device mounted on the shaft of the motor. Such sealing devices are delicate and unreliable. They are poorly adapted to the long-term service required for those installations to which access is difficult, expensive or even dangerous.
The precise object of the present invention is to remedy these drawbacks, and especially to provide an alternating-current electric motor the windings of which can withstand a high voltage and which are easy to produce by virtue of the large distances which separate the windings from each other and the windings from the stator magnetic circuit.
This electric motor is particularly suitable for forming a submerged electric-pump unit.
To this end, the present invention proposes an alternating-current electric motor including a stator magnetic circuit comprising a first part on which electrical windings are mounted and a second, hollow, part within which is mounted a cylindrical rotor equipped with a rotational shaft supported by at least two bearings, which motor is characterized in that it further includes a stator chamber with a leaktight wall, at least a part of which is produced from a non-magnetic insulating material, within which are mounted the first part of the stator magnetic circuit and the electrical windings, the second part of the stator magnetic circuit, the cylindrical rotor and the support bearings lying outside the said chamber and being arranged in such a way that the stator magnetic circuit passes through the wall of the said chamber in the part produced from non-magnetic insulating material.
According to another characteristic of the motor of the invention, with the shaft of the rotor of the said motor being linked mechanically to the shaft of the rotor of a pump, the second part of the stator magnetic circuit, the rotor of the said motor, the support bearings and the rotor of the pump are enclosed in a rotor chamber with a leaktight wall equipped with an inlet and with an outlet for a fluid to be pumped.
According to another characteristic of the motor of the invention, the leaktight wall of the stator chamber includes a device for compensating for the pressure difference between the inside and the outside of the said chamber.
According to another characteristic of the motor of the invention, the stator electrical windings include at least one connection for drawing electrical energy.
According to another characteristic of the motor of the invention, the stator magnetic circuit includes a supplementary electrical winding for drawing electrical energy.
According to another characteristic, the motor of the invention further includes an inlet tapping and an outlet tapping which are mounted on the wall of the stator chamber for connecting an external device for cooling a fluid filling the stator chamber.
According to a final characteristic, the motor of the invention further includes a jacket produced from a non-magnetic insulating material which encases the first part of the stator magnetic circuit, connected in leaktight fashion to the part produced from non-magnetic insulating material of the wall of the chamber in order to render the said chamber leaktight.